The present invention relates to pneumatic conveying systems and in particular to a material blending system in combination with a pneumatic conveying system. The invention is particularly applicable for use in achieving a homogeneous quantity of material such as pellets, powders and granular material.
In particular, the invention relates to an improvement upon prior U.S. Patent Application Ser. No. 444,636 filed Nov. 26, 1982. In that prior application, there is disclosed a blender which combines pneumatic conveying and material blending into a system and method wherein the blender consists of a vessel having a vertically oriented central column open at both ends and spaced from the bottom of the vessel. The vessel includes a bottom inlet which is coaxially aligned with the vertically oriented column. Material to be blended is pneumatically conveyed from a source to the bottom inlet upwardly through the column and is discharged from the top of the column in a geyser-like manner into the vessel. At the same time, material already in the bin flows downwardly through the bin and is entrained in the upwardly flowing gas stream and fresh particulate material to be blended so that the fresh solid particulate and the solid particulate material already in the bin are disbursed on the top of the material to thereby blend or homogenize the material.
In order to achieve a proper blending of material, it is necessary to provide a means for controlling the blender. This control is performed by controlling the flow of material already in the bin downwardly through the bin or vessel to thereby control the quantity of material entrained into the upwardly flowing gas stream.
Prior to the present invention, it was known to utilize a valve arrangement for controlling the flow out of a blending apparatus. U.S. Pat. No. 4,194,845 issued Mar. 25, 1980, utilizes a central column to divide a blending vessel into a pair of outlets with a valve means controlling the flow out of those separate outlets. The object of that invention is to control the quantity of material which is withdrawn from individual portions of the bin and admitted into the conveying gas stream. In this prior patent, a single bin is divided into a plurality of bins by means of baffles. Blending is achieved by withdrawing material from the separate bins at controlled rates. This is similar in concept to the U.S. Pat. No. 3,145,975 issued Aug. 5, 1964.
According to the present invention, blending is achieved by withdrawing material from the entire bin at a uniform rate and allowing this material to be entrained into a stream of fresh material being supplied to the bin.